Mekhanobr-Tekhnika Research and Production, Saint-Petersburg, Russia:

L. A. Vaisberg, Scientific Advisor, Academician of the Russian Academy of Sciences

Petrozavodsk State University, Petrozavodsk, Russia:
E. E. Kameneva, Head of Laboratory, Candidate of Engineering Sciences, kameneva@psu.karelia.ru

It is substantiated that a promising trend in research of the structure, composition and properties of rocks is the nondestructive testing that needs no preliminary preparation of test specimens and ensures quantitative evaluation of structural parameters of the specimens. The article presents the results of the X-ray computed microtomography used to study the microstructure of the basic types of igneous rocks–gabbro diababse and granite. The statistical processing of the microtomography data yields some general relationships and regularities that characterize interconnection of the microstructure parameters. It is found that distribution of pores in the structure of the tested rock specimens is nonuniform; high concentration of pores is typical of feldspars–potash feldspar and plagioclase; in all tested specimens of granite, pores are concentrated in potash feldspar and plagioclase aggregates at the uppermost concentration in potash feldspar; in gabbro diabase pores concentrate mostly in plagioclase; in grains of quartz, actinolite, mica and metallic minerals pores are single or absent. The concentration of pores lowers exponentially as the pores grow in size; there is no unique dependence between porosity and pore concentration, which is connected with the presence of different size pores in the structure of rocks. The role of pores of different size in the general porosity (void content) of the test specimens is nonunique; the void content of the fine-pored specimens is mainly contributed to by the fine-capillary pores; as the size of the pores grows, the contribution of the larger pores in the void content of a specimen increases. Sphericity of pores exponentially decreases as the pores grow in size. A logarithmic dependence is found between the specific areas of pores and mineral grains. The dependence of the strength of rocks on the structural parameters of their pore space is validated. The lower compression strength of granite as against gabbro diabase is connected with the larger size pores of smaller sphericity in granite, which weakens bonding of mineral grains.
The study has been supported by the Russian Science Foundation, Project No. 17-79-30056.

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